Multi-resolution beamforming based on codebooks in mimo systems

ABSTRACT

Certain aspects of the present disclosure relate to methods for beamforming that achieve beamforming optimality criterions. Some proposed beamforming techniques are based on antenna directions with multiple resolutions.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 61/037,139, having Attorney Docket No. 082841P1, filed Mar. 17,2008, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

CROSS REFERENCE TO RELATED APPLICATIONS

The present Application is related by subject matter to Attorney DocketNo. 082841U1, entitled “MULTI-RESOLUTION BEAMFORMING IN MIMO SYSTEMS”filed herewith and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

TECHNICAL FIELD

Certain aspects of the present disclosure generally relate to wirelesscommunication and, more particularly, to beamforming of a transmissionsignal.

BACKGROUND

A dual-mode ultra-wideband (UWB) Physical Layer (PHY) supporting singlecarrier and Orthogonal Frequency Division Multiplexing (OFDM) modulationcan employ a common mode. The UWB PHY may be used for millimeter wave(e.g., with carrier frequency of 60 GHz) communications. The common modeis a single-carrier mode used by both single-carrier and OFDM devicesfor beaconing, network-control signaling, and base-rate datacommunications. The common mode is typically necessary forinteroperability between different devices and different networks.

Millimeter-wave communications may also employ beamforming on one ormore antennas in order to provide both spatial diversity and arraygains. A multitude of antenna configurations such as single antennaelement, sectored antennas, switched antennas, and 1-dimensional (1-D)and 2-dimensional (2-D) antenna arrays may support beamforming.Conventional beamforming, such as Eigen-beamforming, requires channelstate information matrices or beamforming matrices to be fed back to thetransmitting array. The Institute of Electrical and ElectronicsEngineers (IEEE) 802.11n standard specifies feedback information thatincludes row and column sizes of feedback matrices, subcarrier groupingsize (e.g., cluster size), quantization bit size, and an array of actualquantized data elements starting from the lowest subcarrier index to thehighest subcarrier index. For the purpose of beamforming that employspreceding matrices, the feedback information can be reduced by replacingcontents of beamforming matrix with indices of a precoding-matrixcodebook.

Two types of beamforming protocols are considered: an on-demandbeamforming and a pro-active beamforming. On-demand beamforming may beused between two devices (DEVs) or between a piconet controller (PNC)and a device (DEV) and may occur in a channel time allocation (CTA)period allocated to the DEV for the purpose of beamforming. Pro-activebeamforming may be used when the PNC is a source of data to one ormultiple DEVs. This protocol may allow multiple DEVs to train their ownreceiver antennas for preferred reception from the PNC with a loweroverhead.

Two beamforming optimality criterions are considered: a beam switching(steering) and tracking (BST) criterion suitable for all antennaconfigurations, and pattern estimation and tracking (PET) option for 1-Dlinear antenna arrays and 2-D planar antenna arrays. All DEVs thatsupport the PET method may support the BST criterion. The PET criterionmay be used only if the to DEVs that form a communication link supportit. The BST is based on selecting the preferred beam from a given set ofbeams, whereas the PET is based on finding the preferred beam former andcombiner vectors (i.e., antenna weights) that do not necessarily failinto a given set of beam directions.

Therefore, there is a need in the art for methods to efficiently achievebeamforming optimality criterions.

SUMMARY

Certain aspects provide a method for wireless communications. The methodgenerally includes receiving training signals using a first subset of afirst set of codebooks, employing a second subset of the first set ofcodebooks to acquire channel state information (CSI), wherein the secondsubset is same or different than the first subset, estimating a firstpreferred vector of coefficients from the first subset and a secondpreferred vector of coefficients from the second subset, providing, as afeedback to a device, the first preferred vector of coefficients and thesecond preferred vector of coefficients, and using the first preferredvector of coefficients and the second preferred vector of coefficientsto communicate with the device on a transmit direction from a first setof transmit directions.

Certain aspects provide an apparatus for wireless communications. Theapparatus generally includes a receiver for receiving training signalsusing a first subset of a first set of codebooks, a circuit foremploying a second subset of the first set of codebooks to acquirechannel state information (CSI), wherein the second subset is same ordifferent than the first subset, an estimator for estimating a firstpreferred vector of weights from the first subset and a second preferredvector of weights from the second subset, a circuit for providing, as afeedback to a device, the first preferred vector of weights, and acircuit for using the second preferred vector of weights to communicatewith the device on a receive direction from a set of receive directions.

Certain aspects provide an apparatus for wireless communications. Theapparatus generally includes means for receiving training signals usinga first subset of a first set of codebooks, means for employing a secondsubset of the first set of codebooks to acquire channel stateinformation (CSI), wherein the second subset is same or different thanthe first subset, means for estimating a first preferred vector ofweights from the first subset and a second preferred vector of weightsfrom the second subset, means for providing, as a feedback to a device,the first preferred vector of weights, and means for using the secondpreferred vector of weights to communicate with the device on a receivedirection from a set of receive directions.

Certain aspects provide a computer-program product for wirelesscommunications. The computer-program product includes a computerreadable medium encoded with instructions executable to receive trainingsignals using a first subset of a first set of codebooks, employ asecond subset of the first set of codebooks to acquire channel stateinformation (CSI), wherein the second subset is same or different thanthe first subset, estimate a first preferred vector of weights from thefirst subset and a second preferred vector of weights from the secondsubset, provide, as a feedback to a device, the first preferred vectorof weights, and use the second preferred vector of weights tocommunicate with the device on a receive direction from a set of receivedirections.

Certain aspects provide an access point. The access point generallyincludes at least one antenna, a receiver for receiving via the at leastone antenna training signals using a first subset of a first set ofcodebooks, a circuit for employing a second subset of the first set ofcodebooks to acquire channel state information (CSI), wherein the secondsubset is same or different than the first subset, an estimator forestimating a first preferred vector of weights from the first subset anda second preferred vector of weights from the second subset, a circuitfor providing, as a feedback to a device, the first preferred vector ofweights, and a circuit for using the second preferred vector of weightsto communicate with the device on a receive direction from a set ofreceive directions.

Certain aspects provide a method for wireless communications. The methodgenerally includes transmitting training signals using a first subset ofa first set of codebooks, receiving, as a feedback from a device, afirst preferred vector of weights, and using the first preferred vectorof weights to communicate with the device on a transmit direction from afirst set of transmit directions.

Certain aspects provide an apparatus for wireless communications. Theapparatus generally includes a transmitter for transmitting trainingsignals using a first subset of a first set of codebooks, a receiver forreceiving, as a feedback from a device, a first preferred vector ofweights, and a circuit for using the first preferred vector of weightsto communicate with the device on a transmit direction from a first setof transmit directions.

Certain aspects provide an apparatus for wireless communications. Theapparatus generally includes means for transmitting training signalsusing a first subset of a first set of codebooks, means for receiving,as a feedback from a device, a first preferred vector of weights, andmeans for using the first preferred vector of weights to communicatewith the device on a transmit direction from a first set of transmitdirections.

Certain aspects provide a computer-program product for wirelesscommunications. The computer-program product includes a computerreadable medium encoded with instructions executable to transmittraining signals using a first subset of a first set of codebooks,receive, as a feedback from a device, a first preferred vector ofweights, and use the first preferred vector of weights to communicatewith the device on a transmit direction from a first set of transmitdirections.

Certain aspects provide an access point. The access point generallyincludes at least one antenna, a transmitter for transmitting via the atleast one antenna training signals using a first subset of a first setof codebooks, a receiver for receiving via the at least one antenna, asa feedback from a device, a first preferred vector of weights; and acircuit for using the first preferred vector of weights to communicatewith the device on a transmit direction from a first set of transmitdirections.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 illustrates an example wireless communication system, inaccordance with certain aspects of the present disclosure.

FIG. 2 illustrates various components that may be utilized in a wirelessdevice in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates a block diagram of an Asymmetric Antenna System (AAS)in accordance with certain aspects of the present disclosure.

FIG. 4 illustrates a beamforming terminology in accordance with certainaspects of the present disclosure.

FIG. 5 illustrates beams organized in clusters in accordance withcertain aspects of the present disclosure.

FIG. 6 illustrates example operations from a receiver perspective forbeamforming in accordance with certain aspects of the presentdisclosure.

FIG. 6A illustrates example components capable of performing theoperations illustrated in FIG. 6.

FIG. 7 illustrates example operations for updating beamforming andcombining vectors in accordance with certain aspects of the presentdisclosure.

FIG. 7A illustrates example components capable of performing theoperations illustrated in FIG. 7.

FIGS. 8A-8C illustrate four, six, and eight beam patterns, respectivelyfor a four-element antenna array in accordance with certain aspects ofthe present disclosure.

FIG. 9A illustrates a beam pattern comprising six beam patternsgenerated by one-dimensional six-element array in accordance withcertain aspects of the present disclosure.

FIG. 9B illustrates a pair of sector beam patterns in accordance withcertain aspects of the present disclosure.

FIG. 10 illustrates a structure of beamforming capability informationelement (IE) in accordance with certain aspects of the presentdisclosure.

FIG. 11 illustrates example operations for a multi-resolutionbeamforming in accordance with certain aspects of the presentdisclosure.

FIG. 11A illustrates example components capable of performing theoperations illustrated in FIG. 1.

FIG. 12 illustrates example operations for sector-level training inaccordance with certain aspects of the present disclosure.

FIG. 12A illustrates example components capable of performing theoperations illustrated in FIG. 12.

FIG. 13 illustrates example operations for determining preferred sectorsin an Asymmetric Antenna System (AAS) in accordance with certain aspectsof the present disclosure.

FIG. 13A illustrates example components capable of performing theoperations illustrated in FIG. 13.

FIGS. 14A-14D illustrate frame structures used for determining preferredsectors in the AAS in accordance with certain aspects of the presentdisclosure.

FIG. 15 illustrates example operations for determining preferred sectorsin a Symmetric Antenna System (SAS) in accordance with certain aspectsof the present disclosure.

FIG. 15A illustrates example components capable of performing theoperations illustrated in FIG. 15.

FIGS. 16A-16B illustrate frame structures used for determining preferredsectors in the SAS in accordance with certain aspects of the presentdisclosure.

FIG. 17 illustrates example of a pair of clusters comprising a pluralityof beams in accordance with certain aspects of the present disclosure.

FIG. 18 illustrates example operations for dividing preferred sectorsinto clusters of beams in accordance with certain aspects of the presentdisclosure.

FIG. 18A illustrates example components capable of performing theoperations illustrated in FIG. 18.

FIG. 19 illustrates example operations for beam-level training inaccordance with certain aspects of the present disclosure.

FIG. 19A illustrates example components capable of performing theoperations illustrated in FIG. 19.

FIG. 20 illustrates example operations for determining preferred beamsin the AAS in accordance with certain aspects of the present disclosure.

FIG. 20A illustrates example components capable of performing theoperations illustrated in FIG. 20.

FIGS. 21A-21D illustrate frame structures used for determining preferredbeams in the AAS in accordance with certain aspects of the presentdisclosure.

FIG. 22 illustrates example operations for determining preferred beamsin the SAS in accordance with certain aspects of the present disclosure.

FIG. 22A illustrates example components capable of performing theoperations illustrated in FIG. 22.

FIGS. 23A-23B illustrate frame structures used for determining preferredbeams in the SAS in accordance with certain aspects of the presentdisclosure.

FIG. 24 illustrates example operations for beam-tracking in accordancewith certain aspects of the present disclosure.

FIG. 24A illustrates example components capable of performing theoperations illustrated in FIG. 24.

FIG. 25 illustrates a structure of data packet with tracking ability inaccordance with certain aspects of the present disclosure.

FIG. 26 illustrates example operations from a transmitter perspectivefor beamforming in accordance with certain aspects of the presentdisclosure.

FIG. 26A illustrates example components capable of performing theoperations illustrated in FIG. 26.

FIG. 27 illustrates example operations from a transmitter perspectivefor determining preferred transmit directions in accordance with certainaspects of the present disclosure.

FIG. 27A illustrates example components capable of performing theoperations illustrated in FIG. 27.

FIG. 28 illustrates example operations from a receiver perspective fordetermining preferred transmit directions in accordance with certainaspects of the present disclosure.

FIG. 28A illustrates example components capable of performing theoperations illustrated in FIG. 28.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Accordingly, while the aspects of the present disclosure are susceptibleto various modifications and alternative forms, specific exemplaryaspects thereof are shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the disclosure to the particular formsdisclosed, but on the contrary, the disclosure is intended to cover allmodifications, equivalents, and alternatives falling within the scope ofthe disclosure. Like numbers may refer to like elements throughout thedescription of the figures.

It should also be noted that in some alternative implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality andprocedures involved.

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on a single carrier transmission or based on an OrthogonalFrequency Division Multiplexing (OFDM). Aspects disclosed herein may beadvantageous to systems employing Ultra Wide Band (UWB) signalsincluding millimeter-wave signals, wherein a beamforming may beaccomplished using a common mode, i.e., using a single carrier. However,the present disclosure is not intended to be limited to such systems, asother coded signals may benefit from similar advantages.

FIG. 1 illustrates an example of a wireless communication system 100 inwhich aspects of the present disclosure may be employed. The wirelesscommunication system 100 may be a broadband wireless communicationsystem. The wireless communication system 100 may provide communicationfor a number of cells 102, each of which is serviced by a base station104. A base station 104 may be a fixed station that communicates withuser terminals 106. The base station 104 may alternatively be referredto as a piconet controller (PNC), an access point, a Node B or someother terminology.

FIG. 1 depicts various user terminals 106 dispersed throughout thesystem 100. The user terminals 106 may be fixed (i.e., stationary) ormobile. The user terminals 106 may alternatively be referred to asremote stations, access terminals, terminals, subscriber units, mobilestations, stations, user equipment, etc. The user terminals 106 may bewireless devices, such as cellular phones, personal digital assistants(PDAs), handheld devices, wireless modems, laptop computers, personalcomputers, etc.

A variety of algorithms and methods may be used for transmissions in thewireless communication system 100 between the base stations 104 and theuser terminals 106. For example, signals may be sent and receivedbetween the base stations 104 and the user terminals 106 in accordancewith UWB techniques. If this is the case, the wireless communicationsystem 100 may be referred to as an UWB system.

A communication link that facilitates transmission from a base station104 to a user terminal 106 may be referred to as a downlink (DL) 108,and a communication link that facilitates transmission from a userterminal 106 to a base station 104 may be referred to as an uplink (UL)110. Alternatively, a downlink 108 may be referred to as a forward linkor a forward channel, and an uplink 110 may be referred to as a reverselink or a reverse channel.

A cell 102 may be divided into multiple sectors 112. A sector 112 is aphysical coverage area within a cell 102. Base stations 104 within awireless communication system 100 may utilize antennas that concentratethe flow of power within a particular sector 112 of the cell 102. Suchantennas may be referred to as directional antennas.

FIG. 2 illustrates various components that may be utilized in a wirelessdevice 202 that may be employed within the wireless communication system100. The wireless device 202 is an example of a device that may beconfigured to implement the various methods described herein. Thewireless device 202 may be a base station 104 or a user terminal 106.

The wireless device 202 may include a processor 204 which controlsoperation of the wireless device 202. The processor 204 may also bereferred to as a central processing unit (CPU). Memory 206, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 204. A portion of thememory 206 may also include non-volatile random access memory (NVRAM).The processor 204 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 206. Theinstructions in the memory 206 may be executable to implement themethods described herein.

The wireless device 202 may also include a housing 208 that may includea transmitter 210 and a receiver 212 to allow transmission and receptionof data between the wireless device 202 and a remote location. Thetransmitter 210 and receiver 212 may be combined into a transceiver 214.A single or a plurality of transmit antennas 216 may be attached to thehousing 208 and electrically coupled to the transceiver 214. Thewireless device 202 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 202 may also include a signal detector 218 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 214. The signal detector 218 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 202 may alsoinclude a digital signal processor (DSP) 220 for use in processingsignals.

The various components of the wireless device 202 may be coupledtogether by a bus system 222, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

Beamforming System Model

A transceiver that employs the same antenna(s) for both transmission andreception, while a multipath channel to another transceiver isreciprocal, is referred to as a Symmetric Antenna System (SAS). Atransceiver that employs one set of antennas for transmission andanother set of antennas for reception or the multipath channel toanother transceiver is not reciprocal is referred to as an AsymmetricAntenna System (AAS). FIG. 3 illustrates a block diagram of the AAS. Afirst transceiver 302 employs M_(T) transmit antennas and M_(R) receiveantennas. A second transceiver 304 employs N_(T) transmit antennas andN_(R) receive antennas.

Channel model H_(1→2) may be used to express the propagation environmentwhen the first transceiver 302 transmits signals to the secondtransceiver 304. Similarly, channel model H_(2→1) may express thepropagation environment when the transceiver 304 transmits signalsreceived by the transceiver 302. The channel models may be used toexpress any of the possible antenna configurations that may be employedin the related art. Furthermore, the channel models may be used toexpress different transmission protocols. In one aspect of the presentdisclosure, OFDM signaling with a cyclic prefix and a fast Fouriertransform (FFT) of N subcarriers may employ the same channel model as atransmission that is Single Carrier (SC) with a cyclic prefix having aburst length N. In such cases, it is typical to assume that the cyclicprefix is longer than any multipath delay spread between anytransmit-receive pair of antenna elements.

An OFDM symbol stream or SC burst x(t) generated at the firsttransceiver 302 may be expressed as:

$\begin{matrix}{{{x(t)} = {\sum\limits_{k = 0}^{N - 1}{s_{k}{\delta \left( {t - {kT}_{c}} \right)}}}},} & (1)\end{matrix}$

where T_(c) is a sample (or chip) duration, and s_(k) represents thecomplex data. The symbol stream may be modulated by a beamforming vectorof weights w=[_(1,1), w_(1,2), . . . , w_(1,M) _(T) ]^(T) prior to beingtransmitted into a communication channel.

A multiple input multiple output (MIMO) channel may be expressed by afrequency domain Channel State Information (CSI) at an arbitrary n^(th)frequency bin such as:

H_(1→2)(n)∈ C^(M) ^(T) ^(×N) ^(R) ,   (2)

$\begin{matrix}{{{H_{1\rightarrow 2}(n)} = \begin{bmatrix}{h_{1,1}^{1\rightarrow 2}(n)} & {h_{1,2}^{1\rightarrow 2}(n)} & \ldots & {h_{1,N_{R}}^{1\rightarrow 2}(n)} \\{h_{2,1}^{1\rightarrow 2}(n)} & {h_{2,2}^{1\rightarrow 2}(n)} & \ldots & {h_{2,N_{R}}^{1\rightarrow 2}(n)} \\\vdots & \vdots & \ddots & \vdots \\{h_{M_{T},1}^{1\rightarrow 2}(n)} & {h_{M_{T},2}^{1\rightarrow 2}(n)} & \ldots & {h_{M_{T},N_{R}}^{1\rightarrow 2}(n)}\end{bmatrix}},} & (3)\end{matrix}$

where terms h_(i,j) (n) may include both transmit and receive filtering,along with the channel impulse response between the j^(th) transmitantenna of the first transceiver 302 and the i^(th) receive antenna ofthe second transceiver 304, j=1,2, . . . , M_(T) and i=1,2, . . . ,N_(R).

Signals received at the second transceiver 304 may be processed with acombining vector of weights c₂=[c_(2,1) c_(2,2) . . . c_(2,N) _(R) ]^(T)in order to produce a combined baseband signal given by:

y(t)=c ₂ ^(H) [Σs _(k)δ((t−kT _(c))

H _(1→2)(t)w ₁ +b(t)],   (4)

where b(t) is an additive white Gaussian noise (AWGN) vector acrossreceive antennas of the second transceiver 304.

The discrete channel model between a transmitter 306 of the firsttransceiver and a receiver 310 of the second transceiver may beexpressed by a single input single output (SISO) channel as:

$\begin{matrix}{{y_{r} = {{{c_{2}^{H}{\sum\limits_{k = 0}^{L - 1}{H_{k}s_{r - k}w_{1}}}} + {c_{2}b_{i}}} = {{\sum\limits_{k = 0}^{L - 1}{p_{k}s_{r - k}}} + b_{i}^{\prime}}}},} & (5)\end{matrix}$

where p_(k)=c₂ ^(H)H_(k)w₁ and i denotes the sample (or chip) indexwithin an OFDM sample (or a single-carrier burst). The SISO channel maybe characterized by a frequency response at frequency bins n=0,1, . . ., N−1 given by:

p _(n) =c ₂ ^(H) H _(1→2)(n)w ₁.   (6)

The discrete-frequency received signal model may be represented as:

Y _(n) =P _(n) S _(n) +B _(n),   (7)

where [S₀, S₁, . . . , S_(N−1)] is the OFDM data symbol (or the FFT ofthe SC data burst), and [B₀, B₁, . . . , B_(N−1)] is the AWGN vector.

A channel model expressing the channel between a transmitter 312 of thesecond transceiver 304 to a receiver 308 of the first transceiver 302may be given by:

Q _(n) =c ₂ ^(H) H _(2→1)(n)w ₂.   (8)

For both OFDM and SC transmissions, the signal-to-noise ratio (SNR) onthe n^(th) subcarrier (n=0,1, . . . , N−1) in both directions of the AASmay be given by:

$\begin{matrix}\begin{matrix}{{{SNR}_{n}^{1\rightarrow 2} = {\frac{E_{s}{P_{n}}^{2}}{N_{0}} = \frac{E_{s}{{c_{2}^{H}{H_{1\rightarrow 2}(n)}w_{1}}}^{2}}{N_{0}}}},} \\{{SNR}^{2\rightarrow 1} = {\frac{E_{s}{Q_{n}}^{2}}{N_{0}} = {\frac{E_{s}{{c_{1}^{H}{H_{2\rightarrow 1}(n)}w_{2}}}^{2}}{N_{0}}.}}}\end{matrix} & (9)\end{matrix}$

One objective of the system design may be to determine preferredbeamforming vectors w₁ and w₂ and preferred combining vectors c₁ and c₂that maximize an effective SNR (ESNR) constrained by the alphabets ofweight vectors.

The ESNR can be defined as a mapping from the instantaneous SNRs ofsubcarriers given by equation (9) to an equivalent SNR that takes intoaccount a forward error correction (FEC) employed in the system. Thereare various methods that can be used for computing the ESNR, such as:calculation of a mean of SNRs over a plurality of subcarriers, aquasi-static method such as the one commonly used in the 3^(rd)generation partnership project 2 (3GPP2) and 1×EV-DV/DO (Evolution Dataand Video/Data Optimized) communication systems, a capacity effectivesignal-to-interference-plus-noise ratio (SINR) mapping (CESM) also usedin the 3GPP2 and the 1×EV-DV/DO systems, a CESM technique based on aconvex metric that may be employed in the 3GPP2 and the 1×EV-DV/DOsystems, and an exponential effective SINR mapping (EESM) used in the3GPP2 systems.

Different ESNR calculation methods may be utilized for the SC and OFDMsystems. For example, a minimum mean square error (MMSE) based SCequalizer typically has an ESNR that can be approximated by the averageof SNRs over different bursts. However, OFDM may tend to have an ESNRthat may be best approximated using the geometric mean of SNRs overdifferent subcarriers. The various other ESNR calculation methods may befurther configured in order to account for additional parameters, suchas FEC, receiver imperfections, and/or bit-error rate (BER).

Beamforming Terminology

When describing beamforming between two devices, the following notationcan be used. Two devices that are communicating can be referred to asDEV1 and DEV2, for example, DEV1 may be a piconet, controller (PNC) andDEV2 may be a subscriber station. The device number d can be 1 for DEV1and 2 for DEV2.

The term quasi-omni pattern generally relates to the lowest resolutionpattern that covers a very broad area of a region of space of interestaround a device (DEV). A PNC may cover the region of space of interestwith a minimal set of, possibly overlapping, quasi-omni patterns. A setsize equal to one may indicate that the PNC is able to cover the spatialregion of interest with only one quasi-omni pattern, indicating that thePNC is omni-capable. The total number of quasi-omni transmit and receivepatterns of interest for DEV number d can be denoted as I^((d,t)) andI^((d,r)), respectively. The corresponding quasi-omni transmit andreceive patterns can be denoted as Q_(n) ^((d,t)) where n=0,1, . . . ,I^((d,t))−1 for the transmit patterns and Q_(n) ^((d,r)) where n=0,1, .. . , I^((d,r))−1 for the receive patterns. The preferred pair ofquasi-omni transmit and receive patterns for DEV d when communicatingwith the other DEV can be identified by indices i^((d,t)) and i^((d,r)),respectively. The corresponding quasi-omni transmit and receive patternscan be denoted as Q_(i) _((d,t)) ^((d,t)) and Q_(i) _((d,r)) ^((d,r)),respectively. If both devices are SAS devices, the superscripts t and rcan be omitted since same antenna arrays are utilized for bothtransmission and reception. FIG. 4A illustrates example of twoquasi-omni patterns Q₀ and Q₁ for the SAS device.

As used herein, the term sector generally refers to a second levelresolution pattern that covers a relatively broad area of multiplebeams. A sector can cover a set of consecutive or nonconsecutive beamsand different, sectors can overlap. The total number of transmit andreceive sectors of interest for DEV number d can be denoted as J^((d,t))and J^((d,r)), respectively. The corresponding transmit and receivesectors can be denoted as S_(n) ^((d,t)) where n=0,1, . . . ,J^((d,t))−1 for the transmit sectors, and S_(n) ^((d,r)) where n=0,1, .. . , J^((d,r))−1 for the receive sectors. The preferred pair oftransmit and receive sectors for DEV d when communicating with the otherDEV can be identified by indices j^((d,t)) and j^((d,r)), respectively.The corresponding transmit and receive sectors can be denoted as S_(j)_((d,t)) ^((d,t)) and S_(j) _((d,r)) ^((d,r)), respectively. If bothdevices are SAS devices, the superscripts t and r can be omitted. FIG.4B illustrates example of four overlapping sectors S₀, S₁, S₂, S₃ forthe SAS device.

Sectors can be divided into beams as a higher level resolution pattern.The total number of transmit and receive beams of interest for DEVnumber d can be denoted as K^((d,t)) and K^((d,r)), respectively. Thecorresponding transmit and receive beams can be denoted as B_(n)^((d,t)) where n=0,1, . . . , K^((d,t))−1 for the transmit beams, andB_(n) ^((d,r)) where n=0,1, . . . , K^((d,r))−1 for the receive beams.The preferred pair of transmit and receive beams for DEV d whencommunicating with the other DEV can be identified by indices k^((d,t))and k^((d,r)), respectively. The corresponding transmit and receivebeams can be denoted as B_(k) _((d,t)) ^((d,t)) and B_(k) _((d,r))^((d,r)), respectively. If both devices are SAS devices, thesuperscripts t and r can be omitted. FIG. 4C illustrates an example ofan 8-element linear antenna array with eight beams B₀, B₁, . . . , B₇for the SAS device.

Beams can be further divided into high-resolution (HRS) beams as thehighest level of resolution pattern. The total number of transmit andreceive HRS beams of interest for DEV number d can be denoted asL^((d,t)) and L^((d,r)), respectively. The corresponding transmit andreceive HRS beams can be denoted as H_(n) ^((d,t)) where n=0:L^((d,t))−1for the transmit HRS beams, and H_(n) ^((d,r)) where n=0:L^((d,r))−1 forthe receive HRS beams. The preferred pair of transmit and receive HRSbeams for DEV d when communicating with the other DEV can be identifiedby indices l^((d,t)) and l^((d,r)), respectively. The correspondingtransmit and receive HRS beams can be denoted as H_(l) _((d,t)) ^((d,t))and H_(l) _((d,r)) ^((d,r)), respectively. If both devices are SASdevices, the superscripts t and r can be omitted. FIG. 4D illustrates anexample of and 8-element linear antenna array with 16 HRS beams H₀,H₁, .. . , H₁₅ for the SAS device.

In general, the multi-resolution definition of quasi-omni patterns,sectors, beams and HRS beams becomes a multi-level definition, whereeach level may use a set of antenna patterns. Therefore, quasi-omnipatterns may represent a first set of antenna patterns, sectors mayrepresent a second set of antenna patterns, beams may represent a thirdset of antenna patterns preferably derived from the second set ofantenna patterns, and HRS beams may represent a fourth level of antennapatterns preferably derived from the third set of antenna patterns.

For a two-dimensional (2-D) antenna array with K_(x) beams on the x-axisand K_(z) beams on the z-axis, the K_(x) beams along the x-axis may beidentified by indices zero through K_(x)−1 in the direction ofincreasing polar angle and may correspond one-to-one with the beamvectors 0 to K_(x)−1 from the selected x-beam codebook. The K_(z) beamsalong the z-axis may be identified by indices zero through K_(z)−1 inthe direction of increasing polar angle and may correspond one-to-onewith the beam vectors 0 to K_(z)−1 from the selected z-beams codebook.This is further illustrated in FIG. 5 for a 2-D antenna array with eightbeams in each direction.

As used herein, a cluster generally refers to a group of beams around acenter beam. The clustering concept is introduced in order to facilitatetracking of preferred beam directions or in general case to facilitatetracking of preferred antenna patterns (directions). The number ofclusters per sector(s) may be left to the implementer. FIG. 5illustrates examples of clusters of different sizes. Cluster encodingmay be used for DEVs supporting the pattern estimation and tracking(PET) option. For DEVs implementing the beam switching and steeringoption, cluster encoding support may not be required. A cluster may beencoded by an 8-bit filed c7c6c5c4c3c2c1c0. The first three leastsignificant bits, i.e., c2c1c0, may encode the beams in the polar angledirection in reference to FIG. 5, while the second set of three bits,i.e., c5c4c3, may encode the beams in the azimuth angle direction. Thelast set of two bits, c7c6, may specify three different 2-D puncturingpatterns, i.e., different cluster geometrics.

Computing and Tracking Preferred Beamforming and Combining Vectors

Certain aspects of the present disclosure may provide for one or morebeamforming algorithms configured to select the beamforming vectors ofantenna weights (w₁ and w₂) and the combining vectors of antenna weights(c₁ and c₂) that maximize at least one signal-quality parameter, such asan ESNR. In the general AAS case, the first transceiver 302 may transmitknown information to the second transceiver 304, which then derivesmatrices characterizing the channel state information (CSI). Thisenables estimates of w₁ and c₂ to be calculated. The second transceiver304 may transmit known information to the first transceiver 302 in orderto provide the CSI that allows for estimates of w₂ and c₁ to becalculated. Some aspects of the present disclosure may employ known datasymbols, pilot signals, or other training information to be transmittedfor acquiring the CSI. Alternative aspects of the present disclosure mayemploy blind adaptive processing or other techniques utilizing unknowntransmitted data to derive the CSI.

In the case of AAS, both directions of the link may need to be utilizedin order to estimate vectors w₁, w₂, c₂, and c₁. In the case of SAS, thebeamforming vectors w₁ and w₂ and the combining vectors c₂ and c₁ in aparticular direction may be equal. Thus, w₁=w₂ and c₂=c₁, and only onedirection of the link may be employed for calculating vectors w₁, w₂,c₂, and c₁.

FIG. 6 illustrates example operations 600 from a receiver perspectivefor beamforming between a first transceiver and a second transceiver.For example, one transceiver may be a piconet controller (PNC) and theother transceiver may be a piconet subscriber device. At 610, the secondtransceiver (or the second device) may receive a subset of a beamformingcodebook from the first transceiver (or the first device). At 620, thesecond device may employ a subset of a combining codebook to acquire afirst CSI matrix, which may be used to estimate the preferredbeamforming vector w₁ of the first device and the preferred combiningvector c₂ of the second device.

A codebook is a matrix comprising one or more columns wherein eachcolumn denotes a beamforming vector or a combining vector. Thus, eachcolumn may correspond to a particular beam pattern and/or beamdirection. Typically, the set of columns spans the entire space (i.e.,360 degrees).

At 630, the preferred beamforming vector w₁ and the preferred combiningvector c₂ may be estimated and produced. It should be appreciated thatthe terms preferred beamforming vector and preferred combining vectordenote estimates of preferred values, and the optimality of suchestimates may be limited with respect to one or more processingconstraints, including (but not limited to) loss of information due toquantization, simplifying assumptions that sacrifice some accuracyand/or precision in order to reduce computational complexity, andlimited processing time, which may limit the number of iterativecalculations. Other constraints may also apply. For example, in someaspects of the present disclosure, a beamforming and/or combining vectorresulting in a signal-quality metric above a predetermined threshold maybe deemed as the preferred relative to a subset of available vectors.Accordingly, the term “preferred beamforming vector” may be equivalentto preferred beamforming vector, as used herein. Similarly, the term“preferred combining vector” may be equivalent to preferred beamformingvector. The estimation step 630 may employ any of various optimalitycriteria, such as the EESM or the mean SNR.

At 640, the preferred beamforming vector w₁ (and, optionally, thepreferred combining vector c₂) may be sent back to the first device. Forthe AAS, steps 610 to 640 may be repeated wherein the designations of“first device” and “second device” are swapped. Thus, a preferredbeamforming vector w₂ and a preferred combining vector c₁ may be alsoestimated. For the SAS, w₁=w₂ and c₂=c₁.

FIG. 26 illustrates example operations 2600 from a transmitterperspective for beamforming between a first transceiver and a secondtransceiver. At 2610, the first transceiver (or the first device) maytransmit a subset of a beamforming codebook to the second transceiver(or the second device). At 2620, once a preferred beamforming vector w₁is determined at the second device, the first device may receive, as afeedback from the second device, the preferred beamforming vector w₁. At2630, the beamforming vector w₁ may be used at the first device tocommunicate with the second device on a transmit direction (e.g., a beamdirection) from a set of transmit directions.

FIG. 7 illustrates example operations 700 for updating beamforming andcombining vectors. At 710, a subset of a beamforming codebook may bereceived at the second device at a rate lower than the rate employedduring acquisition operations 610-640. At 720, the preferred beamformingvector w₁ and the preferred combining vector c₂ may be updated. At 730,updated beamforming vector w₁ (and, optionally, the updated combiningvector c₂) may be fed back to the first device. For the AAS, steps 710to 730 may be repeated, wherein the designations of “first device” and“second device” are swapped. Thus, the estimates for the preferredbeamforming vector w₂ and the preferred combining vector c₁ may be alsoupdated. For the SAS, w₁=w₂ and c₂=c₁.

Beamforming Codebooks and Beam Patterns

For a uniformly spaced linear antenna array with N elements, the arrayfactor may be defined as:

$\begin{matrix}{{{A(\theta)} = {\sum\limits_{n = 1}^{N}{w_{n}^{{j2}\; \pi \; {n{({d/\lambda})}}\cos \; \theta}}}},} & (10)\end{matrix}$

where d is a spacing between array elements, θ denotes an angle from theaxis of the linear array, λ is a wavelength, and w_(n) is an arrayelement weight of the n^(th) array element. The antenna arraydirectivity may be given by:

$\begin{matrix}{{D = \frac{\max {{A(\theta)}}^{2}}{w^{H} \cdot K \cdot w}},} & (11) \\{where} & \; \\{{K_{n,m} = \frac{\sin \left\lbrack {2\; {\pi \left( {d/\lambda} \right)}\left( {n - m} \right)} \right\rbrack}{2\; {\pi \left( {d/\lambda} \right)}\left( {n/m} \right)}},\mspace{14mu} n,{m = 0},1,\ldots \mspace{14mu},{N - 1.}} & (12)\end{matrix}$

The maximum possible directivity may be D_(Max)=N.

The array factor of a two-dimensional array may be given as:

$\begin{matrix}{{{A\left( {\theta,\varphi} \right)} = {\sum\limits_{m = 1}^{N_{x}}{\sum\limits_{n = 1}^{N_{z}}{w_{m,n}^{{j2}\; {\pi {\lbrack{{{m{({d_{x}/\lambda})}}\sin \; {\theta \cos \varphi}} + {{n{({d_{y}/\lambda})}}{\sin \theta \sin \varphi}}}\rbrack}}}}}}},} & (13)\end{matrix}$

where d_(x) denotes array spacing along the x-axis, d_(z) denotes arrayspacing along the z-axis, N_(x) is a number of elements along thex-axis, N_(y) is a number of elements along the z-axis, and φ is arotation angle from the x-axis. The antenna weights w_(m,n) may beexpressed as w_(m,)=w_(x,m)·w_(z,n), where m=0:N_(x)−1, and n=0:N_(z)−1.Thus, an antenna weight matrix may be expressed by W_(xz)=w_(x)·w_(z)^(T).

In one aspect of the present disclosure, two-dimensional antenna arraysmay be trained by employing codewords along the x-axis and the z-axis.The array factor of a two dimensional array that is separable intoone-dimensional (x-axis and z-axis) array components may be expressedas:

$\begin{matrix}{{{A\left( {\theta,\varphi} \right)} = {{A_{x}\left( {\theta,\varphi} \right)} \cdot {A_{z}\left( {\theta,\varphi} \right)}}},} & (14) \\{where} & \; \\{{{A_{x}\left( {\theta,\varphi} \right)} = {\sum\limits_{n = 1}^{N_{x}}{w_{x,n}^{{j2}\; {\pi {\lbrack{{m{({d_{x}/\lambda})}}{\sin \theta}\; {\cos \varphi}}\rbrack}}}}}},} & (15) \\{{A_{z}\left( {\theta,\varphi} \right)} = {\sum\limits_{n = 1}^{N_{z}}{w_{z,n}{^{{j2\pi}\; {n{({d_{z}/\lambda})}}{\sin \theta \sin \varphi}}.}}}} & (16)\end{matrix}$

Specifically, for the purpose of training, two-dimensional codebooksderived from one-dimensional codebooks (e.g., x-axis and z-axiscodebooks) may be utilized. For example, a two-dimensional codebookW_(xz) ∈ C^(N) ^(x) ^(×N) ^(z) may be expressed using a codebook forone-dimensional antenna arrays along the x-axis, w_(x) ∈ C^(N) ^(x)^(×1) and a codebook for one-dimensional antenna arrays along thez-axis, w_(z) ∈ C^(N) ^(z) ^(×1). For example, two-dimensional antennasweights may be computed from x-axis and z-axis antenna weights, such as:

w _(m,n) =w _(x,m) ·w _(z,n) for m=0:N _(x)−1 and n=0:N _(z)−1   (17)

Certain aspects of the present disclosure may support generating and/oremploying beam codebooks and sector codebooks. A beam codebook, as usedherein, denotes a codebook in which the number of beams may be greaterthan or equal to the number of antennas. A sector codebook, as usedherein, denotes a quasi-omni codebook comprising a number of beams thatmay be less than the number of antennas.

For certain aspects of the present disclosure wherein beam codebooks areemployed for training, it may be sufficient to employ a pair ofone-dimensional beam codebooks instead of a two-dimensional codebook. Inone aspect of the present disclosure, a beam codebook matrix for Nantennas and M beams may be expressed as:

$\begin{matrix}{{W\left( {n,m} \right)} = {{j^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({M/2})}},M})}}}{({M/4})}\rbrack}}\mspace{14mu} {for}\mspace{14mu} n} = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} {and}\mspace{14mu} m}} = {{0\text{:}\mspace{14mu} M} - 1}}}} & (18)\end{matrix}$

wherein fix(·) is a function that returns the integer part of itsargument. In an alternative aspect, the function fix(·) may be replacedwith a function round(·) that rounds its argument to the nearestinteger. It should be appreciated that alternative formulas andfunctions may be employed for calculating elements of a beam codebookmatrix, and that the aspects described herein are intended to illustrateexamples, not limitations, of the claimed disclosure.

FIG. 8A illustrates four beam patterns 801-804 generated by afour-element linear array corresponding to the following codebookmatrix:

$\begin{matrix}{W = {\begin{bmatrix}{+ 1} & {+ 1} & {+ 1} & {+ 1} \\{- 1} & {- j} & {+ 1} & {+ j} \\{+ 1} & {- 1} & {+ 1} & {- 1} \\{- 1} & {+ j} & {+ 1} & {- j}\end{bmatrix}.}} & (19)\end{matrix}$

FIG. 8B illustrates six beam patterns 811-816 generated by afour-element linear array that employs the following codebook matrix:

$\begin{matrix}{W = {\begin{bmatrix}{+ 1} & {+ 1} & {+ 1} & {+ 1} & {+ 1} & {+ 1} \\{- 1} & {- 1} & {- j} & {+ 1} & {+ 1} & {+ j} \\{+ 1} & {+ j} & {- 1} & {+ 1} & {+ j} & {- 1} \\{- 1} & {+ 1} & {- 1} & {+ 1} & {- 1} & {+ 1}\end{bmatrix}.}} & (20)\end{matrix}$

A benefit of employing the beam patterns illustrated in FIG. 8B is thatif the four-element array is in a receiving mode and the strongestreceived signal direction is 45°, the beam pattern 813 (and thus, thearray gain) may achieve maximum in the direction of the strongestreceived signal. If the four beam patterns in FIG. 8A were employed, thestrongest received signal may arrive between beam patterns 801 and 802where the array gain is very low.

The same four-element array may employ alternative codebooks that enableit to generate other beam patterns. For example, FIG. 8C illustrateseight beam patterns 821-828 generated by a four-element linear arraythat employs the following codebook matrix:

$\begin{matrix}{W = {\begin{bmatrix}{+ 1} & {+ 1} & {+ 1} & {+ 1} & {+ 1} & {+ 1} & {+ 1} & {+ 1} \\{- 1} & {- 1} & {- j} & {- j} & {+ 1} & {+ 1} & {+ j} & {+ j} \\{+ 1} & {+ j} & {- 1} & {- j} & {+ 1} & {+ j} & {- 1} & {- j} \\{- 1} & {- j} & {+ j} & {- 1} & {+ 1} & {+ j} & {- j} & {+ 1}\end{bmatrix}.}} & (21)\end{matrix}$

Antenna arrays may employ a variety of codebooks that provide forvarying numbers of beam patterns in order to provide for differentangular resolutions. In one aspect of the present disclosure, trainingmay first employ a low resolution (i.e., fat) beam followed by highresolution (i.e., narrow) beams. In some aspects, a fat beam maycomprise a plurality of narrow beams.

When beam codebooks are employed for training of two-dimensional arrays,beam codebooks for x-axis and z-axis one-dimensional arrays may beemployed for calculating the beam codebook for the two-dimensionalarray. If the x-axis codebook comprises K_(x) beams and the z-axiscodebook comprises K_(z) beams, then the two-dimensional array hasK_(x)·K_(z) beams.

For certain aspects of the present disclosure wherein sector codebooksare employed, sector codebook matrices for N antennas (where N is evennumber) and M=N/2 sectors may be given by:

$\begin{matrix}{{W\left( {n,m} \right)} = \left\{ \begin{matrix}{\left( {- j} \right)^{{mod}{({n,2})}}} & {{m = 0}} \\{\left( {- 1} \right)^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({M/2})}},M})}}}{({M/2})}\rbrack}}} & {{{n = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} m}} = {{1\text{:}\mspace{14mu} M} - 1}}},}}\end{matrix} \right.} & (22)\end{matrix}$

wherein each sector may comprise two beams of a beam codebook having Nbeams. Alternative aspects of the present disclosure may provide forvariations to formulas and functions used to generate sector codebookmatrices. For example, the fix(·) function in equation (22) may bereplaced with a round(·) function. Other variations may be made inaccordance with alternative applications and aspects, as will beappreciated by those skilled in the art.

FIG. 9A illustrates a beam pattern comprising six beam patterns 901-906generated by a one-dimensional six-element array. Sector beam patternsmay be generated by combining beam pairs. For example, a first sectormay comprise beam patterns 901 and 904, a second sector may comprisebeam patterns 902 and 905, and a third sector may comprise beam patterns903 and 906. Thus, sectors may comprise adjacent or non-adjacent beampatterns. Furthermore, sectors may overlap.

FIG. 9B illustrates a pair of sector beam patterns 911 and 912 for alinear six-element antenna array. A corresponding two-sector codebookmay be given by:

$\begin{matrix}{W = {\begin{bmatrix}{+ 1} & {+ 1} \\{+ 1} & {- 1} \\{- j} & {- j} \\{- 1} & {+ 1} \\{+ 1} & {+ 1} \\{- 1} & {+ 1}\end{bmatrix}.}} & (23)\end{matrix}$

In alternative aspects of the present disclosure, sector codebooks maybe also provided for the case when M≠N/2.

Beamforming Optimality Criterions

Two beamforming optimality criterions are proposed in the presentdisclosure: a beam switching (steering) and tracking (BST) criterionsuitable for all antenna configurations, and pattern estimation andtracking (PET) criterion suitable only for one-dimensional (1-D) linearantenna arrays and two-dimensional (2-D) planar antenna arrays. Alldevices (DEVs) that support the PET approach may also support the BST.The PET may be used only if both DEVs that form a communication linksupport this particular criterion.

The BST criterion may be independent of utilized antenna configuration,i.e., the BST may be applied with switched antennas, sectored antennas,and antenna arrays that employ multiple-input multiple-output (MIMO)transmission/reception. It is important to note that the BST does notrequire any knowledge about a codebook used by a particular device(DEV), i.e., a DEV2 does not need to know the codebook used by a DEV1,and the DEV2 does not need to know how many antennas the DEV1 uses.Therefore, the BST represents the beamforming criterion that works withany antenna configuration and with any amount of available informationabout another DEV. The BST criterion is based on selecting a preferredset of patterns at each level of beamforming, as well as on tracking apreferred pattern during a tracking phase. On the other hand, the PETcriterion is based on finding the preferred beam former and combinervectors (i.e., antenna weights) that do not necessarily fall into agiven set of beam patterns.

Beamforming Protocols

Certain aspects of the present disclosure support two beamformingprotocols: an on-demand beamforming protocol and a pro-activebeamforming protocol. The on-demand beamforming may take place within achannel time allocation period (CTAP) allocated to a DEV. A DEV1 mayreserve a CTAP for the special purpose of beamforming acquisition withanother device DEV2. In the pro-active beamforming, the sector leveltraining may take place in the sector training section of a beacon partof a super-frame. The number of sectors at a DEV may be specified, forexample, within the beamforming capability information element (IE), asillustrated in FIG. 10. The DEV may send its beamforming capability IEto a piconet controller (PNC) during or after an association procedure.The PNC may broadcast the beamforming capability IE or may relay it toany other device willing to communicate with the DEV. The messageexchange following the sector-level training and the beam-level trainingmay take place in the beamforming CTAP allocated to the PNC and to theDEV.

In the case of on-demand beamforming, the DEV1 may request a serviceperiod (SP) in order to perform beamforming with DEV2. The SP may beallocated with a special stream index. The SP allocation along with DEV1and DEV2 beamforming capabilities may be broadcasted within thebeamforming capability Information Element (IE). One example of thestructure of the beamforming capability IE is illustrated in FIG. 10.

The beamforming capability IE may specify the number of omni-directionsand sectors at both transmitting and receiving devices. For certainaspects of the present disclosure, if the field “# Tx Q-omni directions”is equal to 1, then a device may be omni-capable on transmission. Also,if the field “# Rx Q-omni directions” is equal to 1, then the device maybe omni-capable on reception. For certain aspects of the presentdisclosure, if the “Antenna array type” field is equal to 0 then aswitched antenna may be utilized, if the “Antenna array type” field isequal to 1 then sectored antennas may be used, if this field is equal to2 then 1-D linear antenna array with antenna spacing of one half of thewavelength may be used, and if this field is equal to 3 then 2-D planarantenna array with antenna spacing of one half of the wavelength may beused. Value 4 of the “Antenna array type” field may be unspecified,while values 5-7 may be reserved.

The beamforming capability IE may comprise information about a maximumnumber of beamforming levels that each device is capable of. Thebeamforming capability IE may also specify a number of transmit andreceive antennas at both transmitting and receiving devices. The “PET”field of the beamforming capability IE may indicate that the patternestimation and tracking procedure based on codebooks may need to be usedfor beamforming. The tracking support may be also provided, asillustrated in FIG. 10.

Multiresolution Beamforming

A two-dimensional transmitter array having, for example, 8×8=64 elementswould typically transmit 64 training sequences in 64 differentdirections specified by 8×8 beamforming codebooks. A two-dimensionalreceiver array having, for example, 6×6=36 elements will receive each ofthe 64 transmissions in 36 different combining directions. Thus,64×36=2304 training sequences are required to identify the preferredtransmit/receive beam pair. This procedure may have prohibitively largeprocessing latency. Certain aspects of the present disclosure support amethod for beamforming that employs multiple resolutions which reducescomputational complexity and processing latency of the beamforming.

For certain aspects of the present disclosure, the transmitter mayemploy a plurality of sector patterns along each of the x-axis and thez-axis. Each sector pattern may comprise a plurality of narrower x-axisand z-axis beam patterns. Once the preferred sector pattern isdetermined, the preferred narrow beam within the sector may bedetermined. Therefore, the number of training sequences required toidentify the preferred transmit/receive beam pair may be substantiallyreduced.

FIG. 11 illustrates example operations 1100 for the multi-resolutionbeamforming. Prior to the beamforming process, a first device and asecond device may exchange antenna array information (not shown), suchas the number of antennas along the z-axis, the number of antennas alongthe x-axis, the number of sectors the first device and the second deviceare going to use during coarse acquisition, the codebook identification(or number of beams) to be used during the beam-level training, and thecodebook identification (or number of HRS beams) to be used during atracking process. Furthermore, before every beamforming process, i.e.,preceding every data session, the first device and the second device mayexchange information about a number of one or more beamforming levels tobe used for that particular data session.

As an exemplary case, a first device (e.g., a piconet controller) and asecond device (e.g., a subscriber device) both have 1-D linear array ofeight elements and employ the same sectoring. When the second deviceassociates with the PNC, the two devices may exchange the followinginformation: number of antennas along the z-axis N_(z)=8, number ofantennas along the x-axis N_(x)=1, number of sectors equal to two,number of beams equal to eight, number of HRS beams for tracking equalto 32, a clustering information such as, for example, that one clustercomprises one beam that is equal to four HRS beams.

At 1110, according to some signal-quality metric, at least one preferredsector pattern may be selected for transmission/reception at the firstdevice and at the second device. This selection process may be referredas a coarse-acquisition process. Each sector pattern may comprise aplurality of beam patterns. For example, one or more sectors used fortransmission may be identified as providing the best signal (as measuredby any combination of signal quality or performance metrics) at areceiver side.

The beam patterns within each selected sector may be grouped intoclusters. Thus, each cluster may comprise a plurality of adjacent beampatterns, which may reside along both the x-axis and the z-axis, andeach sector comprises one or more clusters. Clusters may comprise beamswithin the sector that are selected with respect to any combination ofsignal-quality or performance metrics.

At 1120, at least one preferred beam pattern for transmission and forreception may be selected at the first device and at the second device.This selection process may be referred as the fine acquisition process,and it may also comprise selection of one or more preferred clusterswith respect to any combination of signal-quality or performancemetrics. One or more beams may be selected with respect to anycombination of signal-quality or performance metrics (such as the ESNR)and used for data communications. For certain aspects of the presentdisclosure, preferred beams may be intentionally selected withinnon-adjacent clusters in order to provide more than one separate pathsbetween communicating devices. This may be especially beneficial whenthe preferred beam direction suddenly experience strong loss, and thealternative path is required in order to maintain a signal quality.

At 1130, at least one preferred beam pattern for transmission andreception may be tracked at the first device and at the second device.Tracking may also employ HRS beam codebooks for beams that providehigher resolution than the regular beams. HRS beams may be assigned toeach selected cluster and used for low-rate tracking. Any combination ofperformance criteria may be used to update the selection of which HRSbeam to use, and this re-evaluation process may be performedperiodically at a low rate relative to data transmissions.

FIG. 27 illustrates example operations from a transmitter perspectivefor determining preferred transmit directions in accordance with certainaspects of the present disclosure. At 2710, training signals may betransmitted to a device using a first set of transmit directions. At2720, an indication of at least one first preferred transmit directionderived from the first set of transmit directions may be received fromthe device. At 2730, training signals may be transmitted to the deviceusing a second set of transmit directions, wherein the second set oftransmit directions is derived from the at least one first preferredtransmit direction. At 2740, an indication of at least one secondpreferred transmit direction derived from the second set of transmitdirections may be received from the device. At 2750, the at least onesecond transmit preferred direction may be used to communicate with thedevice.

FIG. 28 illustrates example operations from a receiver perspective fordetermining preferred transmit directions in accordance with certainaspects of the present disclosure. At 2810, training signals transmittedfrom a device using a first set of transmit directions may be received.At 2820, a preferred transmit direction may be derived from the firstset of transmit directions. At 2830, an indication of the preferredtransmit direction to the device may be provided as a feedback to thedevice, wherein the feedback is provided by sweeping through a secondset of transmit directions.

Operations 2700 and 2800 are general examples of multi-resolutionbeamforming. More specific examples of multi-resolution beamforming aredescribed in the following text of the present disclosure.

FIG. 12 illustrates example operations 1200 for four-stage sector-leveltraining in accordance with certain aspects of the present disclosure.At 1210, training of sectors may be performed to determine at least onepreferred sector. At 1220, feedback information may be sent to anotherdevice about the at least one preferred sector. After that, at 1230, asector-to-beam mapping may of the at least one preferred sector intobeams be performed. For example, mapping may be implemented by slicingthe at least one preferred sector into beams. A mapping message sent toanother device may comprise information about a number of transmit andreceive beam directions that this particular device may use in thebeam-level training. Finally, at 1240, acknowledgement information maybe fed back from this device in order to acknowledge a reception of themapping message.

It is important to note that operations 1200 represent a logicaldivision of sector-level training stages, i.e., some of these stages maybe combined together during a communication over a physical wirelesschannel. For example, following the sector-level training stage 1210from a DEV1 to a DEV2, the feedback and mapping messages may be sentcombined from the DEV2 to the DEV1 as a part of the training sequencestransmitted from the DEV2 to the DEV1 (i.e., as a part of thesector-level training stage 1210 from the DEV2 to the DEV1).

FIG. 13 illustrates example operations 1300 for determining preferredsectors in an Asymmetric Antenna System (AAS), and FIGS. 14A-14Dillustrate frame structures broadcasted during the training and feedbackphases. Operations 1300 may also correspond to step 1110 in FIG. 11.Steps 1302-1312 may correspond to the sector training stage 1210 fromFIG. 12, while steps 1314-1320 may correspond to the feedback stage1220. It can be assumed, without loss of generality, that devices mayemploy two-dimensional antenna arrays for both transmission andreception. The total number of transmit and receive antenna elements forDEV number d may be equal to M^((d,t)) and M^((d,r)), respectively. Eachdevice may select its own sector codebooks. Each device may select itsbeam codebooks based on the number of antennas and a predeterminednumber of beams.

At 1302, the first device may transmit in J^((1,t)) cycles a trainingsequence set using J^((1,t)) sectors, as also illustrated in FIG. 14A.Each training sequence from the training sequence set is known at thesecond device and may be based on a pair of Golay sequences. Thetransmissions in each cycle may comprise J^((2,r)) training sequencessent in the same transmit sector of the first device and correspond toall possible receive sectors of the second device. At 1304, the seconddevice may receive, during each cycle, the training sequences usingJ^((2,r)) different sectors. At 1306, based on received trainingsequences, at least one preferred receive sector direction for thesecond device may be determined, and at least one preferred transmitsector direction for the first device may be determined. Preferredsectors may be determined with respect to any combination ofsignal-quality or performance metrics. For certain aspects of thepresent disclosure, at 1302, J^((1,t)) training sequences in each cyclemay be transmitted from the first device using J^((1,t)) differenttransmit sectors in each cycle. All J^((1,t)) training sequences withina cycle may be received at the second device with one out of J^((2,r))different receive sectors, at 1304. In every next cycle, a new receivesector may be employed at the second device, and after J^((2,r)) cyclesall J^((2,r)) receive sectors of the second device may be utilized.

At 1308, the second device may transmit in J^((2,t)) cycles a trainingsequence set using J^((2,t)) sectors, as illustrated in FIG. 14B. Eachtraining sequence from the training sequence set is known at the firstdevice and may be based on a pair of Golay sequences. The transmissionsin each cycle may comprise J^((1,r)) training sequences sent in the sametransmit sector of the second device and correspond to all possiblereceive sectors of the first device. At 1310, the first device mayreceive, during each cycle, the training sequences using J^((1,r))different sectors. At 1312, based on received training sequences, atleast one preferred receive sector direction for the first device may bedetermined, and at least one preferred transmit sector direction for thesecond device may be determined. Preferred sectors may be determinedwith respect to any combination of signal-quality or performancemetrics. For certain aspects of the present disclosure, at 1308,J^((2,t)) training sequences in each cycle may be transmitted from thesecond device using J^((2,t)) different transmit sectors in each cycle.All J^((2,t)) training sequences within a cycle may be received at thefirst device with one out of J^((1,r)) receive sectors, at 1310. Inevery next cycle, a new receive sector may be employed at the firstdevice, and after J^((1,r)) cycles all J^((1,r)) receive sectors of thefirst device may be utilized.

At 1314, the first device may feed back information about at least onepreferred transmit sector direction for the second device bytransmitting the feedback message J^((1,t)) times using J^((1,t))sectors S₀ ^((1,t)), . . . , S_(j) _((1,t)) ^((1,t)), . . . , S_(J)_((1,t)) ⁻¹ ^((1,t)), as also illustrated in FIG. 14C. At 1316, thesecond device may receive and decode information about at least onepreferred transmit sector direction using the preferred receive sectorS_(j) _((2,r)) ^((2,r)), as illustrated in FIG. 14C. For certain aspectsof the present disclosure when the first device is omni-capable,sweeping through all transmit sectors may not be required. At 1318, thesecond device may feed back information about at least one preferredtransmit sector direction for the first device by transmitting thefeedback message using the preferred transmit sector S_(j) _((2,t))^((2,t)), as illustrated in FIG. 14D. At 1320, the first device mayreceive and decode information about at least one preferred transmitsector direction using its preferred receive sector S_(j) _((1,r))^((1,r)), as illustrated in FIG. 14D.

Upon completion of the feedback stage, both devices may know theirpreferred transmit and receive sector(s). The mapping stage may followthe feedback stage, as illustrated in FIG. 12 with the step 1230. Inthis stage, one device may map preferred transmit and receive sector(s)into beams and may send related information to the other device. Uponsuccessful reception of this information, the other device may feed backan acknowledgement message, as illustrated in FIG. 12 with the step1240.

FIG. 15 illustrates example operations for determining preferred sectorsin a Symmetric Antenna System (SAS), and FIGS. 16A-16B illustrate framestructures broadcasted during the training and feedback phases.Operations 1500 may also correspond to step 1110 in FIG. 11. Steps1510-1530 may correspond to the sector training stage 1210 from FIG. 12,while steps 1540-1550 may correspond to the feedback stage 1220. It canbe again assumed, without loss of generality, that devices may employtwo-dimensional antenna arrays for both transmission and reception,while each device utilizes identical antenna arrays for bothtransmission and reception. A first device may comprise atwo-dimensional antenna array having N_(x)×N_(z)=M⁽¹⁾ elements, and asecond device comprises a two-dimensional antenna array havingM_(x)×M=M⁽²⁾ elements. For this aspect of the present disclosure, J⁽¹⁾denotes the number of sectors for the first device, and J⁽²⁾ denotes thenumber of sectors for the second device. Each device may select its ownsector codebooks. Each device may select its beam codebooks based on thenumber of antennas and a predetermined number of beams.

At 1510, the first device may transmit in J⁽¹⁾ cycles a trainingsequence set using J⁽¹⁾ sectors, as illustrated in FIG. 1 6A. Eachtraining sequence from the training sequence set is known at the seconddevice and may be based on a pair of Golay sequences. The transmissionsin each cycle may comprise J⁽²⁾ training sequences sent in the samesector of the first device and correspond to all possible sectors of thesecond device. At 1520, the second device may receive, during eachcycle, the training sequences using J⁽²⁾ different sectors. At 1530,based on received training sequences, at least one preferred sectordirection for the second device may be determined, and at least onepreferred sector direction for the first device may be determined.Preferred sectors may be determined with respect to any combination ofsignal-quality or performance metrics. For certain aspects of thepresent disclosure, at 1510, J⁽¹⁾ training sequences in each cycle maybe transmitted from the first device using J⁽¹⁾ different sectors ineach cycle. All J⁽¹⁾ training sequences within a cycle may be receivedat the second device with one out of J⁽²⁾ sectors, at 1520. In everynext cycle, a new sector may be employed at the second device, and afterJ⁽²⁾ cycles all J⁽²⁾ sectors of the second device may be utilized.

At 1540, the second device may feed back information about at least onepreviously determined preferred sector direction for the first device bytransmitting the feedback message J⁽¹⁾ times using its preferred sectorS_(j) ₍₂₎ ⁽²⁾, as illustrated in FIG. 16B. At 1550, the first device mayreceive and decode information about at least one preferred sectordirection using J⁽¹⁾ sectors S₀ ⁽¹⁾, . . . , S_(j) ₍₁₎ ⁽¹⁾, . . . ,S_(J) ₍₁₎ _(—1) ⁽¹⁾, as illustrated in FIG. 16B.

Upon completion of the feedback stage, both devices may know theirpreferred sector(s). The mapping stage may follow the feedback stage, asillustrated in FIG. 12 with the step 1230. In this stage, one device maymap preferred sector(s) into clusters of beams and into beam patterns,and may also send related information to the other device. Uponsuccessful reception of this information, the other device may feed backan acknowledgement message, as illustrated in FIG. 12 with the step1240.

FIG. 17 illustrates an exemplary case wherein the device selects twopreferred sectors and partitions the sectors into clusters 1710 and1720. Each cluster may comprise a plurality of beams. As illustrated inFIG. 17, a cluster, as used herein, may refer to a set of adjacentbeams. The device may also employ the beam codebooks for mapping thebeams to the sector(s).

FIG. 18 illustrates example operations 1800 for dividing preferredsectors into clusters of beams as a part of the mapping stage 1230 fromFIG. 12. At 1810, a device may divide its preferred transmit and receivesector(s) into at least one cluster of beams. At 1820, the device maysend feedback information to other device that includes a number ofclusters, a number of beams in each cluster, codeword identifiers of thebeams in each cluster, and which beams belong to which clusters.

The other device may also divide its preferred transmit and receivesector(s) into at least one cluster of beams, at 1830, and it mayinform, at 1840, the device about the number of clusters it will useduring beam acquisition, the number of beams per cluster, and codewordidentifiers of beams in each cluster.

FIG. 19 illustrates example operations 1900 for four-stage beam-leveltraining in accordance with certain aspects of the present disclosure.At 1910, training of beams may be performed to determine at least onepreferred beam. At 1920, feedback information may be sent to anotherdevice about the at least one preferred beam. After that, at 1930, asector-to-HRS beam mapping of the at least one preferred beam into HRSbeams may be performed. For example, mapping may be implemented byslicing the at least one preferred sector into beams. A mapping messagesent to another device may comprise information about a number oftransmit and receive HRS beam directions that this particular device mayuse during the tracking phase. Finally, at 1940, acknowledgementinformation may be fed back from this device in order to acknowledge areception of the mapping message.

It is important to note that operations 1900 represent a logicaldivision of beam-level training stages, i.e., some of these stages maybe combined together during a communication over a physical wirelesschannel. For example, following the beam-level training stage 1910 froma DEV1 to a DEV2, the feedback and mapping messages may be sent combinedfrom the DEV2 to the DEV1 as a part of the training sequencestransmitted from the DEV2 to the DEV1 (i.e., as a part of the beam-leveltraining stage 1910 from the DEV2 to the DEV1).

FIG. 20 illustrates example operations 2000 for determining preferredbeams within sectors in the AAS, and FIGS. 21A-21D illustrate framestructures broadcasted during the training and feedback phases.Operations 2000 may also correspond to step 1120 in FIG. 11. Steps2002-2012 may correspond to the beam training stage 1910 from FIG. 19,while steps 2014-2020 may correspond to the feedback stage 1920.

At 2002, the first device may transmit in K^((1,t)) cycles a trainingsequence set using K^((1,t)) beams, as illustrated in FIG. 21A. Eachtraining sequence from the training sequence set is known at the seconddevice and may be based on a pair of Golay sequences. The transmissionsin each cycle may comprise K^((2,r)) training sequences sent in the sametransmit beam of the first device and correspond to all possible receivebeams of the second device. At 2004, the second device may receive,during each cycle, the training sequences using K^((2,r)) differentbeams. At 2006, based on received training sequences, at least onepreferred receive beam direction for the second device may bedetermined, and at least one preferred transmit beam direction for thefirst device may be determined. Preferred beams may be determined withrespect to any combination of signal-quality or performance metrics. Forcertain aspects of the present disclosure, at 2002, K^((1,t)) trainingsequences in each cycle may be transmitted from the first device usingK^((1,t)) different transmit beams in each cycle. All K^((1,t)) trainingsequences within a cycle may be received at the second device with oneout of K^((2,r)) receive beams, at 2004. In every next cycle, a newreceive beam may be employed at the second device, and after K^((2,r))cycles all K^((2,r)) receive beams of the second device may be utilized.

At 2008, the second device may transmit in K^((2,t)) cycles a trainingsequence set using K^((2,t)) beams, as illustrated in FIG. 21B. Eachtraining sequence from the training sequence set is known at the firstdevice and may be based on a pair of Golay sequences. The transmissionsin each cycle may comprise K^((1,r)) training sequences sent in the sametransmit beam of the second device and correspond to all possiblereceive beams of the first device. At 2010, the first device mayreceive, during each cycle, the training sequences using K^((1,r))different beams. At 2012, based on received training sequences, at leastone preferred receive beam direction for the first device may bedetermined, and at least one preferred transmit beam direction for thesecond device may be determined. Preferred beams may be determined withrespect to any combination of signal-quality or performance metrics. Forcertain aspects of the present disclosure, at 2008, K^((2,t)) trainingsequences in each cycle may be transmitted from the second device usingK^((2,t)) different transmit beams in each cycle. All K^((2,t)) trainingsequences within a cycle may be received at the first device with oneout of K^((1,r)) receive beams. In every next cycle, a new receive beammay be employed at the first device, and after K^((1,r)) cycles allK^((1,r)) receive beams of the first device may be utilized.

At 2014, the first device may feed back information about at least onepreferred transmit beam direction for the second device by transmittingthe feedback message using the preferred transmit sector S_(j) _((1,t))^((1,t)) chosen in the sector-level training, as illustrated in FIG.21C. At 2016, the second device may receive and decode information aboutat least one preferred transmit beam direction using the preferredreceive sector S_(j) _((2,r)) ^((2,r)), as illustrated in FIG. 21C. At2018, the second device may feed back information about at least onepreferred transmit beam direction for the first device by transmittingthe feedback message using the preferred transmit beam B_(k) _((2,t))^((2,t)), as illustrated in FIG. 21D, or the preferred transmit sectorS_(j) _((2,t)) ^((2,t)) chosen in the sector-level training. At 2020,the first device may receive and decode information about at least onepreferred transmit beam direction using the preferred receive beam B_(k)_((1,r)) ^((1,r)), as illustrated in FIG. 21D, or using the preferredreceive sector S_(j) _((1,r)) ^((1,r)) chosen in the sector-leveltraining.

Upon completion of the feedback stage, both devices may know theirpreferred transmit and receive beam(s). The mapping stage may follow thefeedback stage, as illustrated in FIG. 19 with the step 1930. In thisstage, one device may map preferred transmit and receive beam(s) intohigh-resolution beams and may send related information to the otherdevice. Upon successful reception of this information, the other devicemay feed back an acknowledgement message, as illustrated in FIG. 19 withthe step 1940.

In addition to the beam-acquisition procedure where the preferred beamsare determined at both devices, the first device may also adapt thenumber of beams in one or more clusters and transmit those changes tothe second device. For example, the first device may reduce the numberof beams in each cluster. The first device may transmit this informationusing its preferred transmit beam. The second device may receive thisinformation using its preferred receive beam and feeds back anacknowledgment message.

FIG. 22 illustrates example operations for determining preferred beamsfor transmission/reception in the SAS, and FIGS. 23A-23B illustrateframe structures broadcasted during the training and feedback phases.Operations 2200 may also correspond to step 1120 in FIG. 11. Steps2210-2230 may correspond to the beam training stage 1910 from FIG. 19,while steps 2240-2250 may correspond to the feedback stage 1920. Forthis aspect of the present disclosure, K⁽¹⁾ denotes the number of beamsfor the first device, and K⁽²⁾ denotes the number of beams for thesecond device.

At 2210, the first device may transmit in K⁽¹⁾ cycles a trainingsequence set using K⁽¹⁾ beams, as illustrated in FIG. 23A. Each trainingsequence from the training sequence set is known at the second deviceand may be based on a pair of Golay sequences. The transmissions in eachcycle may comprises K⁽²⁾ training sequences sent in the same beam of thefirst device and correspond to all possible beams of the second device.At 2220, the second device may receive, during each cycle, the trainingsequences using K⁽²⁾ different beams. At 2230, based on receivedtraining sequences, at least one preferred beam direction for the seconddevice may be determined, and at least one preferred beam direction forthe first device may be determined. Preferred beams may be determinedwith respect to any combination of signal-quality or performancemetrics. For certain aspects of the present disclosure, at 2210, K⁽¹⁾training sequences in each cycle may be transmitted from the firstdevice using K⁽¹⁾ different beams in each cycle. All K⁽¹⁾ trainingsequences within a cycle may be received at the second device with oneout of K⁽²⁾ beams. In every next cycle, a new beam may be employed atthe second device, and after K⁽²⁾ cycles all K⁽²⁾ beams of the seconddevice may be utilized.

At 2240, the second device may feed back information about at least onepreviously determined preferred beam direction for the first device bytransmitting the feedback message using the preferred sector S_(j) ₍₂₎⁽²⁾ chosen in the sector-level training, as illustrated in FIG. 23B. At2250, the first device may receive and decode information about at leastone preferred beam direction using the preferred sector S_(j) ₍₁₎ ⁽¹⁾chosen in the sector-level training, as illustrated in FIG. 23B.

Upon completion of the feedback stage, both devices may know theirpreferred beam(s). The mapping stage may follow the feedback stage, asillustrated in FIG. 19 with the step 1930. In this stage, one device maymap preferred beam(s) into high-resolution beams and may send relatedinformation to the other device. Upon successful reception of thisinformation, the other device may feed back an acknowledgement message,as illustrated in FIG. 19 with the step 1940.

FIG. 24 illustrates example operations 2400 for beam-tracking, and FIG.25 illustrates a structure of packets with tracking ability. Operations2400 may also correspond to step 1130 in FIG. 11. A first device may beconfigured to send data packets to a second device, wherein both thefirst device and the second device comprise antenna arrays. Operations2400 can be applied for tracking of beams in the SAS, as well as fortracking of the preferred transmit beam and the preferred receive beamof the first device and the second device, respectively in the AAS.Terms ‘first device’ and ‘second device’ may be also swapped in thiscase, and operations 2400 can be applied for tracking of the preferredtransmit beam and the preferred receive beam of the second device andthe first device, respectively. Tracking procedure may be also performedon high-resolution beams providing the highest resolution for updatingthe preferred directions for transmission and reception.

At 2410, the first device may construct tracking packets with abeam-tracking bit in each tracking packet to indicate that each trackingpacket contains a training sequence used for tracking. For example, apacket with its beam-tracking bit set to “1” may indicate that it is atracking packet. One example of the packet structure is illustrated inFIG. 25. For example, a tracking packet 2510 that includes the beamtracking bit may comprise a training sequence (TS) 2512, followed by aGuard Time (GT) slot 2514, and a data packet 2516.

At 2420, the first device may transmit a plurality of L^((2,r)) trackingpackets, where L^((2,r)) is a number of beams within a cluster of asecond device. All L^((2,r)) data packets may be transmitted from thefirst device using the preferred beam B_(j) _((1,t)) ^((1,t)) (datapackets 2516 and 2526 of the tracking packets 2510 and 2520,respectively in FIG. 25), and all L^((2,r)) training sequences may betransmitted using a beam B₁ ^((1,t)) within a cluster of the firstdevice (training sequences 2512 and 2522 in FIG. 25). At 2430, thesecond device may receive L^((2,r)) data packets using the preferredbeam B_(j) _((2,r)) ^((2,r)), and may receive L^((2,r)) trainingsequences using all L^((2,r)) beams within the cluster.

This process may be repeated for each beam in the cluster of the firstdevice. After L^((1,t)) cycles, where L^((1,t)) is a total number ofbeams in the cluster of the first device, the first device may transmit,at 2440, L^((2,r)) data packets using the preferred beam B_(j) _((1,t))^((1,t)) (data packets 2536 and 2546 of the tracking packets 2530 and2540, respectively in FIG. 25), and all L^((2,r)) training sequences maybe transmitted using a beam B_(L) _((1,t)) ^((1,t)) within the cluster(training sequences 2532 and 2542 in FIG. 25). Following that, at 2450,the second device may receive L^((2,r)) data packets using the preferredbeam B_(j) _((2,r)) ^((2,r)), and may receive L^((2,r)) trainingsequences using all L^((2,r)) beams in the cluster.

At 2460, the second device may determine a preferred pair of beams forthe first device and for the second device. If this particular pair ofbeams has better signal quality than the current preferred pair of beamsused for data transmission/reception, then, at 2470, the second devicemay reshape the cluster around a new preferred beam and send feedbackinformation to the first device about the preferred pair of beams. At2480, the first device may receive information about the preferred pairof beams, may switch to a new preferred beam for data transmission, andmay reshape the cluster around the new preferred beam. At 2490, thefirst device may inform the second device about a new number of beams inthe reshaped cluster of the first device. Steps 2420-2490 may berepeated for a plurality of sets of tracking packets.

The scope of the disclosure should not be interpreted as being limitedto the array processing aspects illustrated herein. Rather, theApplicants anticipate that alternative aspects may comprise antennaarrays with more than eight elements along a particular axis and antennaarrays comprising antennas with a plurality of polarizations, and thatsuch antenna-array configurations fall within the scope of thedisclosure. In one aspect, two dipole antennas with orthogonal linearpolarizations may be employed together to produce a quasi-omni pattern.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrate circuit (ASIC), or processor. Generally,where there are operations illustrated in Figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering. For example, blocks 610-640, 710-730,1110-1130,1210-1240, 1302-1320, 1510-1550, 1810-1840, 1910-1940,2002-2020, 2210-2250, 2410-2490, 2610-2630, 2710-2750, and 2810-2830,illustrated in FIGS. 6, 7, 11, 12, 13, 15, 18, 19, 20, 22, 24, 26, 27,and 28 correspond to circuit blocks 610A-640A, 710A-730A, 1110A-1130A,1210A-1240A, 1302A-1320A, 1510A-1550A, 1810A-1840A, 1910A-1940A,2002A-2020A, 2210A-2250A, 2410A-2490A, 2610A-2630A, 2710A-2750A, and2810A-2830A, illustrated in FIGS. 6A, 7A, 11A, 12A, 13A, 15A, 18A, 19A,20A, 22A, 24A, 26A, 27A, and 28A.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware or any combination thereof If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

The techniques provided herein may be utilized in a variety ofapplications. For certain aspects, the techniques presented herein maybe incorporated in an access point or other type of wireless device withprocessing logic and elements to perform the techniques provided herein.

1. A method for wireless communications, comprising: receiving trainingsignals using a first subset of a first set of codebooks; employing asecond subset of the first set of codebooks to acquire channel stateinformation (CSI), wherein the second subset is same or different thanthe first subset; estimating a first preferred vector of weights fromthe first subset and a second preferred vector of weights from thesecond subset; providing, as a feedback to a device, the first preferredvector of weights; and using the second preferred vector of weights tocommunicate with the device on a receive direction from a set of receivedirections.
 2. The method of claim 1, wherein the first preferred vectorof weights from the first subset of the first set of codebooks and thesecond preferred vector of weights from the second subset of the firstset of codebooks are determined based on a signal-quality metric.
 3. Themethod of claim 2, wherein the signal-quality metric comprises aneffective signal-to-noise ratio (ESNR) at the device.
 4. The method ofclaim 1, further comprising: receiving beamforming capabilityinformation from the device either directly or via a piconet controller(PNC), wherein the beamforming capability information comprises anindication if codebooks are used for beamforming, a total number of Ntransmit antennas, and a total number of M transmit directions from afirst set of transmit directions.
 5. The method of claim 4, wherein thefirst set of codebooks is employed for transmitting the training signalsusing transmit directions from the first set of transmit directions. 6.The method of claim 5, wherein the first set of codebooks is representedin a matrix form for the total of N transmit antennas and the total of Mtransmit directions from the first set of transmit directions as:${W\left( {n,m} \right)} = {{j^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({M/2})}},M})}}}{({M/4})}\rbrack}}\mspace{14mu} {for}\mspace{14mu} n} = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} {and}\mspace{14mu} m}} = {{0\text{:}\mspace{14mu} M} - 1}}}$wherein fix(·) is a function that returns the integer part of itsargument.
 7. The method of claim 4, wherein a second set of codebooks isemployed for transmitting the training signals using transmit directionsfrom a second set of transmit directions, wherein transmit directionsfrom the first set of transmit directions have higher resolution thantransmit directions from the second set of transmit directions.
 8. Themethod of claim 7, wherein the second set of codebooks is represented ina matrix form for the total number of N transmit antennas, N is an evennumber and P=N/2 transmit directions from the second set of transmitdirections as: ${W\left( {n,m} \right)} = \left\{ \begin{matrix}{\left( {- j} \right)^{{mod}{({n,2})}}} & {{m = 0}} \\{\left( {- 1} \right)^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({P/2})}},P})}}}{({P/2})}\rbrack}}} & {{n = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} m}} = {{1\text{:}\mspace{14mu} P} - 1}}}}\end{matrix} \right.$ wherein each transmit direction from the secondset of transmit directions comprises two transmit directions from thefirst set of transmit directions of a codebook from a first set ofcodebooks having N transmit directions from the first set of transmitdirections, and wherein fix(·) is a function that returns the integerpart of its argument.
 9. The method of claim 1, wherein at least a partof each training signal is based on Golay sequences.
 10. An apparatusfor wireless communications, comprising: a receiver for receivingtraining signals using a first subset of a first set of codebooks; acircuit for employing a second subset of the first set of codebooks toacquire channel state information (CSI), wherein the second subset issame or different than the first subset; an estimator for estimating afirst preferred vector of weights from the first subset and a secondpreferred vector of weights from the second subset; a circuit forproviding, as a feedback to a device, the first preferred vector ofweights; and a circuit for using the second preferred vector of weightsto communicate with the device on a receive direction from a set ofreceive directions.
 11. The apparatus of claim 10, wherein the firstpreferred vector of weights from the first subset of the first set ofcodebooks and the second preferred vector of weights from the secondsubset of the first set of codebooks are determined based on asignal-quality metric.
 12. The apparatus of claim 11, wherein thesignal-quality metric comprises an effective signal-to-noise ratio(ESNR) at the device.
 13. The apparatus of claim 10, further comprising:a receiver for receiving beamforming capability information from thedevice either directly or via a piconet controller (PNC), wherein thebeamforming capability information comprises an indication if codebooksare used for beamforming, a total number of N transmit antennas, and atotal number of M transmit directions from a first set of transmitdirections.
 14. The apparatus of claim 13, wherein the first set ofcodebooks is employed for transmitting the training signals usingtransmit directions from the first set of transmit directions.
 15. Theapparatus of claim 14, wherein the first set of codebooks is representedin a matrix form for the total of N transmit antennas and the total of Mtransmit directions from the first set of transmit directions as:${W\left( {n,m} \right)} = {{j^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({M/2})}},M})}}}{({M/4})}\rbrack}}\mspace{14mu} {for}\mspace{14mu} n} = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} {and}\mspace{14mu} m}} = {{0\text{:}\mspace{14mu} M} - 1}}}$wherein fix(·) is a function that returns the integer part of itsargument.
 16. The apparatus of claim 13, wherein a second set ofcodebooks is employed for transmitting the training signals usingtransmit directions from a second set of transmit directions, whereintransmit directions from the first set of transmit directions havehigher resolution than transmit directions from the second set oftransmit directions.
 17. The apparatus of claim 16, wherein the secondset of codebooks is represented in a matrix form for the total number ofN transmit antennas, N is an even number and P=N/2 transmit directionsfrom the second set of transmit directions as:${W\left( {n,m} \right)} = \left\{ \begin{matrix}{\left( {- j} \right)^{{mod}{({n,2})}}} & {{m = 0}} \\{\left( {- 1} \right)^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({P/2})}},P})}}}{({P/2})}\rbrack}}} & {{n = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} m}} = {{1\text{:}\mspace{14mu} P} - 1}}}}\end{matrix} \right.$ wherein each transmit direction from the secondset of transmit directions comprises two transmit directions from thefirst set of transmit directions of a codebook from a first set ofcodebooks having N transmit directions from the first set of transmitdirections, and wherein fix(·) is a function that returns the integerpart of its argument.
 18. The apparatus of claim 10, wherein at least apart of each training signal is based on Golay sequences.
 19. Anapparatus for wireless communications, comprising: means for receivingtraining signals using a first subset of a first set of codebooks; meansfor employing a second subset of the first set of codebooks to acquirechannel state information (CSI), wherein the second subset is same ordifferent than the first subset; means for estimating a first preferredvector of weights from the first subset and a second preferred vector ofweights from the second subset; means for providing, as a feedback to adevice, the first preferred vector of weights; and means for using thesecond preferred vector of weights to communicate with the device on areceive direction from a set of receive directions.
 20. The apparatus ofclaim 19, wherein the first preferred vector of weights from the firstsubset of the first set of codebooks and the second preferred vector ofweights from the second subset of the first set of codebooks aredetermined based on a signal-quality metric.
 21. The apparatus of claim20, wherein the signal-quality metric comprises an effectivesignal-to-noise ratio (ESNR) at the device.
 22. The apparatus of claim19, further comprising: means for receiving beamforming capabilityinformation from the device either directly or via a piconet controller(PNC), wherein the beamforming capability information comprises anindication if codebooks are used for beamforming, a total number of Ntransmit antennas, and a total number of M transmit directions from afirst set of transmit directions.
 23. The apparatus of claim 22, whereinthe first set of codebooks is employed for transmitting the trainingsignals using transmit directions from the first set of transmitdirections.
 24. The apparatus of claim 23, wherein the first set ofcodebooks is represented in a matrix form for the total of N transmitantennas and the total of M transmit directions from the first set oftransmit directions as:${W\left( {n,m} \right)} = {{j^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({M/2})}},M})}}}{({M/4})}\rbrack}}\mspace{14mu} {for}\mspace{14mu} n} = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} {and}\mspace{14mu} m}} = {{0\text{:}\mspace{14mu} M} - 1}}}$wherein fix(·) is a function that returns the integer part of itsargument.
 25. The apparatus of claim 22, wherein a second set ofcodebooks is employed for transmitting the training signals usingtransmit directions from a second set of transmit directions, whereintransmit directions from the first set of transmit directions havehigher resolution than transmit directions from the second set oftransmit directions.
 26. The apparatus of claim 25, wherein the secondset of codebooks is represented in a matrix form for the total number ofN transmit antennas, N is an even number and P=N/2 transmit directionsfrom the second set of transmit directions as:${W\left( {n,m} \right)} = \left\{ \begin{matrix}{\left( {- j} \right)^{{mod}{({n,2})}}} & {{m = 0}} \\{\left( {- 1} \right)^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({P/2})}},P})}}}{({P/2})}\rbrack}}} & {{n = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} m}} = {{1\text{:}\mspace{14mu} P} - 1}}}}\end{matrix} \right.$ wherein each transmit direction from the secondset of transmit directions comprises two transmit directions from thefirst set of transmit directions of a codebook from a first set ofcodebooks having N transmit directions from the first set of transmitdirections, and wherein fix(·) is a function that returns the integerpart of its argument.
 27. The apparatus of claim 19, wherein at least apart of each training signal is based on Golay sequences.
 28. Acomputer-program product for wireless communications, comprising acomputer readable medium encoded with instructions executable to:receive training signals using a first subset of a first set ofcodebooks; employ a second subset of the first set of codebooks toacquire channel state information (CSI), wherein the second subset issame or different than the first subset; estimate a first preferredvector of weights from the first subset and a second preferred vector ofweights from the second subset; provide, as a feedback to a device, thefirst preferred vector of weights; and use the second preferred vectorof weights to communicate with the device on a receive direction from aset of receive directions.
 29. An access point, comprising: at least oneantenna; a receiver for receiving via the at least one antenna trainingsignals using a first subset of a first set of codebooks; a circuit foremploying a second subset of the first set of codebooks to acquirechannel state information (CSI), wherein the second subset is same ordifferent than the first subset; an estimator for estimating a firstpreferred vector of weights from the first subset and a second preferredvector of weights from the second subset; a circuit for providing, as afeedback to a device, the first preferred vector of weights; and acircuit for using the second preferred vector of weights to communicatewith the device on a receive direction from a set of receive directions.30. A method for wireless communications, comprising: transmittingtraining signals using a first subset of a first set of codebooks;receiving, as a feedback from a device, a first preferred vector ofweights; and using the first preferred vector of weights to communicatewith the device on a transmit direction from a first set of transmitdirections.
 31. The method of claim 30, further comprising: transmittingbeamforming capability information to the device either directly or viaa piconet controller (PNC), wherein the beamforming capabilityinformation comprises an indication if codebooks are used forbeamforming, a total number of N transmit antennas, and a total numberof M transmit directions from the first set of transmit directions. 32.The method of claim 31, wherein the first set of codebooks is employedfor transmitting the training signals using transmit directions from thefirst set of transmit directions.
 33. The method of claim 32, whereinthe first set of codebooks is represented in a matrix form for the totalof N transmit antennas and the total of M transmit directions from thefirst set of transmit directions as:${W\left( {n,m} \right)} = {{j^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({M/2})}},M})}}}{({M/4})}\rbrack}}\mspace{14mu} {for}\mspace{14mu} n} = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} {and}\mspace{14mu} m}} = {{0\text{:}\mspace{20mu} M} - 1}}}$wherein fix(·) is a function that returns the integer part of itsargument.
 34. An apparatus for wireless communications, comprising: atransmitter for transmitting training signals using a first subset of afirst set of codebooks; a receiver for receiving, as a feedback from adevice, a first preferred vector of weights; and a circuit for using thefirst preferred vector of weights to communicate with the device on atransmit direction from a first set of transmit directions.
 35. Theapparatus of claim 34, further comprising: a transmitter fortransmitting beamforming capability information to the device eitherdirectly or via a piconet controller (PNC), wherein the beamformingcapability information comprises an indication if codebooks are used forbeamforming, a total number of N transmit antennas, and a total numberof M transmit directions from the first set of transmit directions. 36.The apparatus of claim 35, wherein the first set of codebooks isemployed for transmitting the training signals using transmit directionsfrom the first set of transmit directions.
 37. The apparatus of claim36, wherein the first set of codebooks is represented in a matrix formfor the total of N transmit antennas and the total of M transmitdirections from the first set of transmit directions as:${W\left( {n,m} \right)} = {{j^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({M/2})}},M})}}}{({M/4})}\rbrack}}\mspace{14mu} {for}\mspace{14mu} n} = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} {and}\mspace{14mu} m}} = {{0\text{:}\mspace{14mu} M} - 1}}}$wherein fix(·) is a function that returns the integer part of itsargument.
 38. An apparatus for wireless communications, comprising:means for transmitting training signals using a first subset of a firstset of codebooks; means for receiving, as a feedback from a device, afirst preferred vector of weights; and means for using the firstpreferred vector of weights to communicate with the device on a transmitdirection from a first set of transmit directions.
 39. The apparatus ofclaim 38, further comprising: means for transmitting beamformingcapability information to the device either directly or via a piconetcontroller (PNC), wherein the beamforming capability informationcomprises an indication if codebooks are used for beamforming, a totalnumber of N transmit antennas, and a total number of M transmitdirections from the first set of transmit directions.
 40. The apparatusof claim 39, wherein the first set of codebooks is employed fortransmitting the training signals using transmit directions from thefirst set of transmit directions.
 41. The apparatus of claim 40, whereinthe first set of codebooks is represented in a matrix form for the totalof N transmit antennas and the total of M transmit directions from thefirst set of transmit directions as:${W\left( {n,m} \right)} = {{j^{{fix}{\lbrack\frac{n \times {{mod}{({{m + {({M/2})}},M})}}}{({M/4})}\rbrack}}\mspace{14mu} {for}\mspace{14mu} n} = {{{0\text{:}\mspace{14mu} N} - {1\mspace{14mu} {and}\mspace{14mu} m}} = {{0\text{:}\mspace{14mu} M} - 1}}}$wherein fix(·) is a function that returns the integer part of itsargument.
 42. A computer-program product for wireless communications,comprising a computer readable medium encoded with instructionsexecutable to: transmit training signals using a first subset of a firstset of codebooks; receive, as a feedback from a device, a firstpreferred vector of weights; and use the first preferred vector ofweights to communicate with the device on a transmit direction from afirst set of transmit directions.
 43. An access point, comprising: atleast one antenna; a transmitter for transmitting via the at least oneantenna training signals using a first subset of a first set ofcodebooks; a receiver for receiving via the at least one antenna, as afeedback from a device, a first preferred vector of weights; and acircuit for using the first preferred vector of weights to communicatewith the device on a transmit direction from a first set of transmitdirections.